Abstract: Nickel is a critical strategic non-ferrous metal widely used in electroplating, aerospace, new energy batteries, and other industries. However, Ni–EDTA complex wastewater has become a major challenge in industrial heavy-metal wastewater treatment due to its highly stable six-coordinate chelate structure. The stability constant of Ni–EDTA reaches 18.56, making it far more stable than common nickel complexes such as those with citrate or tartrate. Conventional treatment processes, including neutralization, coagulation, and precipitation, cannot effectively break the coordination bonds, leading to not only the loss of valuable nickel resources but also significant ecological risks. The released nickel ions can accumulate in human organs and aquatic organisms, posing long-term threats to both human health and water ecosystem stability. The synergistic technology that integrates decomplexation with resource recovery aligns with the new environmental governance paradigm of pollution-reduction and carbon-emission synergy, offering outstanding techno-economic value and representing a key direction in environmental engineering and resource recycling. Based on the structural stability of Ni–EDTA and the water-quality characteristics of typical wastewater, which often contains high concentrations of chemical oxygen demand, hypophosphite, total phosphorus, and coexisting metal ions such as copper under strongly acidic conditions, this paper systematically elucidates the core principles and process mechanisms underlying decomplexation and resource recovery. It comprehensively reviews the research progress of three mainstream technical routes: chemical oxidation or reduction decomplexation coupled with nickel recovery, electrochemical decomplexation–electrodeposition integration, and metal displacement-driven decomplexation–precipitation recovery. For each route, the paper analyzes performance advantages and limiting factors, including decomplexation efficiency, nickel recovery rate and product purity, energy and chemical consumption, secondary pollution, and engineering scalability. Chemical oxidation decomplexation, especially various Fenton-based processes, is mature and widely applicable, achieving decomplexation rates exceeding 99% under optimized conditions; however, it suffers from high chemical consumption and generation of iron-containing sludge. Electrochemical technology enables in-situ decomplexation and direct recovery of metallic nickel without chemical addition, with energy consumption significantly reduced when using three-dimensional porous cathodes or flow-through electrode reactors; however, it is limited by mass-transfer constraints, electrode corrosion, and passivation, particularly at low nickel concentrations or in high-salt wastewater. Displacement decomplexation operates under mild conditions with low cost and almost no secondary pollution, achieving excellent nickel-removal efficiency in processes such as Fe³⁺ substitution combined with chelating precipitation or MOF-mediated ligand exchange; however, it is hindered by relatively slow reaction kinetics and difficulties in large-scale preparation of functional materials. Through multi-dimensional comparison of coordination bond-breaking efficiency, nickel recovery rate, energy and chemical costs, and engineering applicability under different water-quality conditions and concentration ranges, the paper clarifies the applicable boundaries and engineering transformation value of each technology. Finally, key future development directions are proposed, including the rational design of targeted decomplexation functional materials with enhanced selectivity and activity, mass-transfer intensification and intelligent upgrading of electrochemical systems through advanced electrode and reactor design, construction of hierarchical multi-technology synergistic processes for complex wastewater matrices, high-value nickel resource recovery beyond conventional hydroxide or oxide products coupled with closed-loop reagent recycling, and the embedding of multi-parameter online sensing and digital twin-based intelligent control systems for dynamic optimization and fault prediction. This review provides theoretical support and decision-making references for the research, development, process selection, and engineering practice of efficient, low-carbon, and high-value treatment technologies for Ni–EDTA wastewater.